Variable Venturi type carburetor

ABSTRACT

A variable Venturi type carburetor is provided with an air chamber arranged between a fuel metering orifice and Venturi section and being in communication with the Venturi section through a second orifice, said air chamber being connected to an air passage which is in communication with both the interior of an air cleaner and atmosphere for introducing a compensating air into the air chamber. The aforesaid air passage has an air metering means consisting of an orifice and a needle. The needle is connected to a bellows which is expansible in response to the atmospheric density so that the needle can control, in cooperation with the associated orifice, the quantity of compensating air to be fed into the air chamber in response to the atmospheric density for obtaining a desirable air/fuel ratio. Since the compensating air is supplied from inside the air cleaner and from atmosphere in a predetermined proportion, desirable air compensation can be effected over the entire range of engine operation from a high speed range to a low speed range.

United States Patent Otani 5] Dec. 9, 1975 VARIABLE VENTURI TYPECARBURETOR [57] ABSTRACT [75] Inventor: Tadahiko Otani, Katsuta, Japan Avariable Venturi type carburetor is provided with an 7 3] AsslgneaHitachi Ltd Japan air chamber arranged between a fuel metering orificeFiledi M y 5, l974 and Venturi section and being in communication with[2]] App NO 470 277 the Venturi section through a second orifice. saidair I chamber being connected to an air passage which is incommunication with both the interior of an air cleaner [30] ForeignApplication Priority Data and atmosphere for introducing a compensatingair May 18, 1973 Japan 48-54567 into the air chamber- The afomsaid airPassage air metering means consisting of an orifice and a nee- [52] US.Cl. 261/39 A; 261/44 R; 261/12] B dle. The needle is connected to abellows which is ex- [5 1] Int. Cl. FOZM 9/06 pansible in response tothe atmospheric density so that [58] Fi ld f S h u 261/39 A, 44 R, 12 Bthe needle can control, in co-operation with the associated orifice, thequantity of compensating air to be {56] References Cit d fed into theair chamber in response to the atmo- UNITED STATES PATENTS sphericdensity for obtaining a desirable air/fuel ratio. 1,636,480 7/1927 Mocket al '26l/39 A the comgesanngt alr lshsuppped g 115K184 i 1,8023214/1931 Mabee et a1 261/121 B cealwr a Tnosp ere m i 2,387,676 10/1945Phillips 26l/39 A propomoh des'rable compensano can 3493217 2/1970 Farm,H H 261/44 R fected over the entire range of engine operation from3,764,120 10/1973 lmai 26l/44 R a high Speed range to a low speed range-3,83l,9l0 8 l974 Shadboltuu 261/39 A 3,836,128 9/l974 Lunsford 261/39 A9 Claims, 4 Drawing Figures Primary Examiner-Tim R. Miles Attorney,Agent, or F1'rmCraig & Antonelli l29 AIR 5 ll US. Patent Dec. 9, 1975Sheet 10f2 3,925,521

FIG. I

PRIOR ART F l G. 2

PRIOR ART 7 7717 I 7 1 '1' 9 H I U.S. Patent Dec. 9, 1975 Sheet 2 of23,925,521

III IIITI FIG. 4

To AIR CHAMBER VARIABLE VENTURI TYPE CARBURETOR BACKGROUND OF THEINVENTION This invention relates to a variable Venturi type (or airvalve type) carburetor for use in an internal combustion engine and,more particularly, to a carburetor provided with a compensatingmechanism which is operable depending on the atmospheric density.

Today, the allowable quantity of harmful ingredients contained in theautomobile exhaust gas is legally regulated. In order to purify and makeharmless the harmful ingredients, it is already known an exhaust gaspurifying device in which an air is injected into the exhaust system tomake the exhaust harmful ingredients harmless. To maintain theperformance of such an exhaust gas purifying device, it is necessary tomaintain the optimum mixing ratio of air to fuel fed into the enginecylinder. One known means to maintain the optimum air/fuel ratio is avariable Venturi type carburetor. This carburetor comprises a carburetormain body having an induction passage formed therein, a pistonreciprocably arranged to project into said induction passage for forminga Venturi section, means responsive to the pressure present in saidVenturi section to displace said piston for maintaining the pressure inthe Venturi section at a substantially constant level, fuel meteringmeans consisting of an orifice fixed in the carburetor main body and aneedle attached to said piston, and means for supplying fuel into saidfuel metering means. With this carburetor, the piston is displaced inresponse to the quantity of intake air into the engine cylinder andhence the needle comprised in the fuel metering means is displaced withrespect to the orifice to thereby change the opening area of the orificefor controlling the quantity of supply fuel. Thus, an air/fuel mixturehaving a substantially constant air/fuel ratio can be obtained bycontrolling the position of the piston and hence the opening areadefined between the orifice and needle depending on the quantity ofintake air into the engine cylinder.

In use of such a variable Venturi type carburetor, if it is initiallyadjusted so as to obtain an air/fuel ratio which is most suitable forpurifying the exhaust harmful ingredients in a level ground driving,then a difficulty will be encountered in a high land driving due to areduced air density. Because, in a high altitude, the quantity of airflowing into the engine cylinder will be reduced even when the pressurein the Venturi section remains unchanged, and accordingly the air/fuelmixture fed into the engine cylinder will become lean (or the mixturewill contain a richer fuel). This will cause the exhaust gas purifyingdevice to fail to maintain desired performance.

To eliminate this difficulty, it was been proposed to provide theforegoing variable Venturi type carburetor with a device forcompensating the fuel discharge quantity depending on the altitude.According to this device, the fuel metering means is provided with anair chamber so arranged between the Venturi section and orifice that theair chamber is in communication with said Venturi section through asecond orifice and an air cleaner through means for supplying a quantityof air depending on the altitude.

The compensating device will be described in more detail with referenceto the accompanying drawings, wherein:

FIG. I is a schematic view of a prior art variable Venturi typecarburetor equipped with an air density compensating device of a typewhich introduces an air density compensating air from the air cleaner;

FIG. 2 is a schematic view of the main portion of another prior art airdensity compensating device of the type which introduces an air densitycompensating air from atmosphere;

FIG. 3 is a schematic view of the variable Venturi type carburetoraccording to one embodiment of this invention; and

FIG. 4 is a schematic view of the main portion of the air densitycompensating device for use in the variable Venturi type carburetoraccording to another embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding ofthis invention, a conventional variable Venturi type carburetor will bedescribed with reference to FIGS. 1 and 2.

Indicated at l is a carburetor main body provided with a throttle valve3 for controlling the air/fuel mixture flowing through an inductionpassage 2. A suction piston 5 is slidably and air-tightly received in asuction chamber in contact with the suction chamber wall 4. The suctionpiston 5 has a suction hole 7 formed therein for introducing into thesuction chamber 8 a negative pressure developed by the intake airflowing through a Venturi section 6. An atmospheric pressure acts on theunderside of a suction piston disc 9 through an air introducing port 12.The suction piston 5 slides up and down to a position where the productof the negative pressure within the suction chamber 8 and the pressurereceiving area of the suction piston 5 balances with the sum of theweight of suction piston 5 and a force applied by a suction pistonspring 13. The suction piston 5 is normally displaced so that thenegative pressure in the Venturi section 6 is kept substantiallyconstant. To the bottom end of the suction piston S is fixed a taperedjet needle 10 so that it extends into an orifice 17 formed in thecarburetor main body 1. When the suction piston 5 moves in the suctionchamber 8, the jet needle 10 moves up and down through the orifice 17 tothereby change the opening area or fuel flowing area of the orifice 17for metering the flow quantity of the fuel, which is supplied from afloat chamber 14 into the orifice 17 via a fuel passage 15. Between theorifice l7 and Venturi section 6 is defined an air chamber 16 which isin communication with the Venturi section 6 via an orifice 11. The airchamber 16 is also in communication with an air cleaner 19 via airpassages 18 and 18A. At the junction of these air passages 18 and 18A isplaced air metering means consisting of a tapered valve body 21 and aneck portion 22. Said valve body 21 is connected to a bellows 20 whichis positioned in a chamber 30 and expansible in response to the pressurein the chamber 30. The chamber 30 is fluidically connected to theinterior of the air cleaner 19 so that the pressure in the chamber 30 issubstantially identical with the atmospheric pressure. Therefore, thebellows 20 is expanded or compressed in response to the atmosphericpressure. The valve body 21 is so contoured that when the bellows 20 isexpanded in response to the reduction in the aunospheric pressure, theopening area defined between the valve body 21 and neck portion 22increases. With such an arrangement, during driving an automobile on ahigh land, the bellows 20 is expanded in response to the reduction inthe atmospheric pressure to thereby increase the air passing area .atthe neck portion 22, so that an increased amount of air is allowed toflow from the air cleaner section into the air chamber 16 of the fuelmetering section. As a result, the quantity of fuel fed into the Venturisection 6 is reduced, permitting to compensate the reduced airproportion in the air/fuel mixture which might otherwise be caused dueto reduction in the air density at a high altitude. The air supplyquantity into the air chamber 16 is controlled mainly depending on theopening area of the neck portion 22 and, therefore, the configuration ofvalve body 21 and the expansible range of bellows 20 are selected sothat an optimum opening area can be obtained depending on theatmospheric pressure.

It has been found, however, that a difficulty is encountered inintroducing a compensating air from the air cleaner 19 into the airchamber 16 because the rate of compensation varies depending on the highspeed operation range and the low speed operation range of the engine.More specifically, if the air passing area defined between the valvebody 21 and narrowed portion 22 has been preset so as to allow anoptimum compensation at a low speed range depending on the atmosphericpressure, then the effect of compensation will be reduced at a highspeed range even when the air passing area is remained unchanged,thereby reducing the proportion of air in the air/fuel mixture. It seemsthat this is because in a high speed range, the pressure in the aircleaner is lowed due to its resistance which becomes greater as theintake air increases in quantity, thereby hindering the supply of asufficient amount of compensating air through passages 18 and 18A intothe air chamber 16, though in the high speed range the piston is movedup to thereby increase the opening area defined between the orifice l1and needle and, hence, compensating air introduced into the air chamber16 should be increased in quantity. On the contrary, if the device hasbeen preset so as to obtain an optimum supply rate of the compensatingair in a high speed operation range, then an excessive amount ofcompensating air will be introduced in a low operation range.

To supply a sufficient quantity of compensating air even in a highoperation range, an air passage 18B communicating with the air meteringmeans is directly communicated with atmosphere by way of a filter 24 asshown in FIG. 2. With this arrangement, however, it has been found thatthe supply quantity of the compensating air excessively increases,thereby increasing the air proportion in the air/fuel mixture in thehigh speed operation range. Thus, a desirable compensation cannot beattained over the entire operation range covering from high speed to lowspeed operation range.

It is therefore a primary object of this invention to provide acarburetor which can compensate the variation in air/fuel ratio due tothe variation in atmospheric pressure over the entire operation range ofan engine from low to high speed operation range, for maintaining adesirable air/fuel ratio.

Another object of this invention is to provide a carburetor which isoperative to compensate for the variation in air/fuel ratio due to thevariation in air density, for maintaining a desirable air/fuel ratio.

Still another object of this invention is to provide a carburetor whichis operative to compensate for the variation in air/fuel ratio due tothe variation in temperature, for maintaining a desirable air/fuelratio.

The variable Venturi type carburetor of this invention is characterizedin that the fuel metering device consisting of an first orifice and aneedle is provided with an air chamber which is located between theVenturi section and the first orifice and in communication with theVenturi section via a second orifice, and the pressure within said airchamber is varied by varying the quantity of compensating air fed intothe air chamber, for compensating the discharge quantity of fuel. Theair chamber is in communication with the air cleaner and atmosphere byway of an air metering means, for introducing the compensating air bothfrom atmosphere and from air cleaner into said air chamber. The airpassages communicating the air metering means with the air cleaner andatmosphere are respectively provided with a flow controlling meansadapted to control the proportion of compensating air from atmosphereand air cleaner. In this manner, a proper amount of compensating air canbe introduced into the air chamber both from atmosphere and from aircleaner over the entire engine operation range covering from low to highspeed operation range.

The air metering means is connected to bellows expansible depending onthe atmospheric pressure for varying the opening area depending on theatmospheric pressure. Thus, the quantity of compensating air fed intothe air chamber is varied depending on the atmospheric pressure, therebyallowing to compensate the variation in air/fuel ratio. The bellows maybe either evacuated or filled with a gas. In the latter case, thebellows may be expansible in response not only to the atmosphericpressure but also to the atmospheric temperature. ln other words, thebellows filled with a gas is responsive to the variation of air densitydue to the variation in both atmospheric pressure and temperature,thereby allowing to compensate the variation in air/fuel ratio caused bythe variation in air density. When suitably held by suitable means whichis operative in response to the temperature, the bellows of the type isresponsive only to the variation in temperature to vary the quantity ofcompensating air into the air chamber, thereby allowing to compensatethe variation in air/fuel ratio caused by the variation in temperature.

Now, the invention will be described with reference to FIGS. 3 and 4illustrating preferred embodiments of this invention. In these Figureslike or equivalent components and portions are designated by likereference numerals to FIGS. 1 and 2. According to this invention thecarburetor is provided with a passage 25 communicating with the aircleaner and another passage 26 communicatin g with atmosphere by way ofa filter 24. Both of these passages 25 and 26 are air passagescommunicating with a chamber 30 in which a bellows 20 is received. Thecompensating air is therfore supplied into the air chamber 16 from theair cleaner 19 through the passage 25 and also from atomsphere throughthe passage 26. The passages 25 and 26 have neck portions 27 and 28,respectively, which are so selected as to provide a preselected airpassing ratio therebetween to thereby predetermine the ratio of the airquantities passing through these passages 27 and 28.

With the foregoing arrangement, when an automobile is driven on a highland, the bellows will be expanded in response to the variation inatmospheric pressure to thereby widen the air metering area definedbetween the valve body 21 and neck portion 22 for introducing theair-density compensating air from the air cleaner l9 and atmosphere. Inthis case, if the neck portion 27 in the passage 25 is selected so as togive a wider cross section that the neck portion 28 in the passage 26,then a smaller quantity of compensating air than that required will besupplied in the high speed operation range; on the other hand, if theneck portion 28 is selected so as to give a wider cross section than theneck portion 27, then a larger quantity of compensating air than thatrequired will be supplied in the high speed operation range. More,specially, when an equal negative pressure is applied to both the neckportions 27 and 28, of which the portion 27 has a wider cross sectionthan the portion 28, then the pressure within the air cleaner [9 will belowered in the higher speed operation range, because of the resistanceof the air cleaner 19, so that the quantity of air passing through thenarrowed portion 27 will be reduced. Since the air passing through theneck portion 28 is also small in quantity due to a reduced cross sectionof the narrowed cross section of the portion 28, then the total quantityof air supplied into the air chamber 16 will be reduced. On thecontrary, when the neck portion 28 has a wider cross section than theneck portion 27, the air passing through the narrowed portion 27 issmall in quantity and an excessive quantity of compensating air issupplied from atmosphere via the neck portion 28 in the high speedoperation range, so that the total quantity of air supplied into the airchamber 16 will be increased in the high speed operation range.

it will be appreciated from the foregoing that by suitably selecting theneck portions 27 and 28, any desired quantity of compensating air can besupplied into the air chamber 16 in the high speed operation range. Solong as the neck portions 27 and 28 are so selected as to givesufficiently larger cross sections than the fuel metering area definedbetween the jet needle and nozzle 1 1, no difficulty will be encounteredin compensation in the low and medium speed operation ranges because thepressure drop within the air cleaner 19 due to its resistance can beneglected in such operation ranges. Similar effects may conveniently beattained by use of the air passing resistance of the passages 25 and 26instead of provision of narrowed portions 27 and 28. By introducing thedensity compensating air from the air cleaner and atmosphere, thepresent invention provides a constant compensation in a wide operationrange covering from low to high speed operation range.

Due to its inferior vibration resistivity, the bellows 20 may have adanger of being damaged easily or entail a varied compensationcharacteristic because of the engine oscillation. To eliminate thisdanger the bellows 20 may be separated from the carburetor and mountedas a single unit together with the chamber 30, orifice 21 and neckportion 22 on the car body at any suitable position free fromoscillation. The attachment of the filter 24 integrally to said unitwill also be preferred for making the entire construction compact.

As is mentioned previously, the bellows 20 may be either evacuated orfilled with any suitable gas. A vacuum bellows will provide theaforesaid actions by expanding and contracting in response only to thepressure within the chamber 30 (this pressure is almost equal to theatmospheric pressure). The atmospheric density varies not only with theatmospheric pressure but also with the atmospheric temperature. Thisnecessitates the compensation also with respect to the variation of airdensity due to the temperature change. If a temperature sensitivesubstance such as alcohol is filled into the bellows 20, then thebellows 20 will be expanded and contracted depending on the temperaturechange even when the atmospheric pressure remains unchanged, therebyallowing to compensate the variation in air density due to the variationin atmospheric temperature.

FlG. 4 illustrates another embodiment of this invention, wherein acontainer 31 is fixed to the bottom of the chamber 30. The container 31is filled with a temperature sensitive substance 29 such as wax andslidably receiving therein a piston 32 which holds the bellows 20. Withthe foregoing arrangement, the temperature sensitive substance 29expands in response to the temperature and displace the valve body 21together with the bellows 20 to thereby control the compensating air fedinto the air chamber. By the use of such an arrangement, the quantity ofcompensating air can be controlled irrespective of the variation in airdensity, and therefore the fluctuation of the air/fuel ratio may becompensated for, which might otherwise be caused when the fuel dischargequantity varies upon variation in the viscous resistance of the fueldepending on the temperature.

What is claimed is:

l. A variable Venturi type carburetor which consists of a carburetormain body having an induction passage extending through it and connectedto an air cleaner, a piston movably arranged so as to project into saidinduction passage for thereby forming a Venturi section, meansresponsive to the pressure in said Venturi section to move the pistonfor thereby maintaining the pressure in the Venturi section at asubstantially constant level, fuel metering means consisting of anorifice integrally formed in the carburetor main body and a needlemounted to said piston, and means for supplying the fuel into said fuelmetering means, characterized by a small chamber arranged between saidorifice and Venturi section so as to be in communication with saidVenturi section through a second orifice; air metering means incommunication with said small chamber; a first air passage communicatingsaid air metering means with said air cleaner; a second air passagecommunicating said air metering means with atmosphere, atmosphericdensity sensitive means responsive to the atmospheric density to operatesaid air metering means; and wherein said first and second air passagesare respectively provided with means for controlling the air passingresistance.

2. A variable Venturi type carburetor according to claim 1, wherein saidmeans for controlling the air passing resistance are neck portions.

3. A variable Venturi type carburetor according to claim I, wherein saidair metering means consists of an orifice and needle, and saidatmospheric density means is a bellows having one end fixed and theopposite end connected to said needle.

4. A variable Venturi type carburetor according to claim 3, wherein saidbellows is received in a second chamber which is in communication withboth said air metering means and first and second air passages.

5. A variable Venturi type carburetor according to claim 4, wherein saidbellows is evacuated.

6. A variable Venturi type carburetor according to claim 4, wherein saidbellows in filled with a gas.

7. A variable Venturi type carburetor according to claim 1, wherein saidair metering means and atmospheric density sensitive means are separatedfrom the 8 claim 8, wherein said temperature sensitive means consists ofa container filled with wax which is expansible in response to thetemperature and a piston slidably received in said container.

1. A VARIABLE VENTURI TYPE CARBURETOR WHICH CONSISTS OF A CARBURETORMAIN BODY HAVING AN INDUCTION PASSAGE EXTENDING THROUGH IT AND CONNECTEDTO AN AIR CLEANER, A POSTON MOVABLY ARRANGED SO AS TO PROJECT INTO SAIDINDUCTION PASSAGE FOR THEREBY FORMING A VENTURI SECTION, MEANSRESPONSIVE TO THE PRESSURE IN SAID VENTURI SECTION AT ASUBSTANMAINTAINING THE PRESSURE IN THE VENTURI SECTION AT ASUBSTANTIALLY CONSTANT LEVEL, FUEL METERING MEANS CONSISTNG OF ANORIFICE INTEGRALLY FORMED IN THE CARBURETOR MAIN BODY AND A NEEDLEMOUNTED TO SAID PISTON, AND MEANS FOR SUPPLYING THE FUEL INTO SAID FUELMETERING MEANS, CHARACTERIZED BY A SMALL CHAMBER ARRANGED BETWEEN SAIDORIFICE AND VENTURI SECTION SO AS TO BE IN COMMUNICATION WITH SAIDVENTURI SECTION THROUGH A SECOND ORIFICE; AIR METERING MEANS INCOMMUNICATION WITH SAID SMALL CHAMBER; A FIRST AIR PASSAGE COMMUNICATIONSAID AIR METERING MEANS WITH SAID AIR CLEANER; A SECOND AIR PASSAGECOMMUNICATING SAID AIR METERING MEANS WITH ATMOSPHERE; ATMOSPHERICDENSITY SENSITIVE MEANS RESPONSIVE TO THE ATMOSPHERIC DENSITY TO OPERATESAID AIR METERING MEANS; AND WHEREIN SAID FIRST AND SECOND AIR PASSAGEARE RESPECTIVELY PROVIDED WITH MEANS FOR CONTROLLING THE AIR PASSAGERESISTANCE.
 2. A variable Venturi type carburetor according to claim 1,wherein said means for controlling the air passing resistance are neckportions.
 3. A variable Venturi type carburetor according to claim 1,wherein said air metering means consists of an orifice and needle, andsaid atmospheric density means is a bellows having one end fixed and theopposite end connected to said needle.
 4. A variable Venturi typecarburetor according to claim 3, wherein said bellows is received in asecond chamber which is in communication with both said air meteringmeans and first and second air passages.
 5. A variable Venturi typecarburetor according to claim 4, wherein said bellows is evacuated.
 6. Avariable Venturi type carburetor according to claim 4, wherein saidbellows in filled with a gas.
 7. A variable Venturi type carburetoraccording to claim 1, wherein said air metering means and atmosphericdensity sensitive means are separated from the carburetor main body andmounted on the car body at a suitable position free from oscillation. 8.A variable Venturi type carburetor according to claim 4, wherein saidbellows is held by means responsive to the temperature.
 9. A variableVenturi type carburetor according to claim 8, wherein said temperaturesensitive means consists of a container filled with wax which isexpansible in response to the temperature and a piston slidably receivedin said container.